The present invention relates generally to dial illumination means which can be used with compasses and is more specifically directed to an improved compass illuminating arrangement utilizing a miniature electrical battery in circuit with a light-emitting-diode (LED) for illuminating the bezel/dial of lensatic magnetic compasses such as the type made by Stocker-Yale Company of Beverly, Mass. That company supplies a magnetic type compass to the U.S. Army, which compass is differently illuminated but whose basic components are governed by the Military Specification MIL-C-10436L and is further identified by a national stock number NSN 6605-00-151-5337.
Presently, all of the U.S. Army lensatic magnetic compasses are illuminated by a plurality of usually seven radioactive tritium-excited phosphor tubes containing a total of approximately 120 millicuries of the tritium gas which has a half-life of 12.26 years. Although the quantity and type of radiation is not harmful, unless taken internally, the problem and disadvantages thereof reside in the cost of handling or processing the old and/or broken compasses for burial of the tritium vials or tubes, and the attendant time and expense of procuring replacement compasses. Presently, the tritium tubes or vials housed within the compass cases last about six years and must be shipped to a radioactive burial ground for disposal, with no present cost-effective means for salvaging or repairs of defective parts. Thus the government is forced to spend between $200,000 and $300,000 annually for their disposal and approximately another $2.5 million annually to procure 100,000 new compasses.
By redesigning the lensatic compass according to the present invention with the unique placement of the non-radioactive and non-magnetic LED illuminating means in a manner which will facilitate cost-effective replacement of defective or damaged parts, the aforestated problems are overcome whereby many of the original compasses will become repairable and can be recycled back into service at a great savings of manhours and related costs.
The current existing form of lensatic magnetic compass generally is a well constructed sturdy instrument which is simple to use. However, the majority of the returned compasses for disposal are caused by mechanical failures or breakage of lens brackets, immobilized dials and broken crystal bezels much of which result from improper soldier handling attributable to excessive forced openings and closings. A lot of the breakage could be prevented with greater pre-use instruction, and most of the mechanical failures could be repaired if sent to a properly instituted and staffed compass repair center where they could be properly screened, repaired and recycled. More particularly a redesigned type of compass with a modified ultra light case embodying the present innovative generally central location of a readily replaceable non-magnetic miniature wafer battery, a non-magnetic LED, and non-magnetic microswitch, thereby eliminating the tritium tubes and related radioactive costly disposal and repurchasing problems and expense, not only would provide an even sturdier and lighter weight compass less susceptible to damage, but one which could be more easily and cost effectively repaired and recycled.
Considering the prior art more particularly, the use of incandescent bulbs to light compasses is, of course, old in the art as is exemplified by patents such as U.S. Pat. Nos. 2,738,412; 3,786,571; and 4,341,023. In each of these patents, the incandescent bulb is energized by an external more substantial electrical power source connected thereto by a power line. A soldier in the field, of course, does not have such power sources available to him. Moreover, incandescent bulbs tend to be somewhat unreliable under field conditions in that they are susceptible to shock damage primarily due to the rough treatment that any equipment receives in the field as well as to the hazards of proximate explosions. U.S. Pat. No. 2,237,963 discloses a compass in combination with a flashlight, wherein a compass is illuminated by a separate bulb powered by the batteries of the flashlight. Again, the bulb disclosed is an incandescent bulb with the attendant disadvantages of an incandescent bulb. In addition, the batteries are standard flashlight batteries which have magnetic properties and can deflect the compass needle or compass rose from true North. Almost all incandescent bulbs emit too much light, require excessive current and must be shielded, filtered or otherwise modified so as to be used effectively with military field compasses.
U.S. Pat. No. 4,115,994 discloses the concept of utilizing a light emitting diode to illuminate the dial of a wrist watch; however, this illumination is not suitable for a military compass in that it presents an extensive illuminated area which can interfere with night vision as well as possibly pinpoint the user as a target.
The present lensatic compass used by the Army uses the aforesaid tritium excited phosphor gas tubes or vials which suffer not only the aforementioned disadvantage of disposal problems and replacement cost, but also lose their luminosity prematurely with age. Additionally, the dial and markings are often difficult to see at night due to low luminosity.
In view of the aforementioned considerations, it is seen that there is a need for a military compass which does not have the numerous drawbacks inherent in compasses of the prior art.